It's set in Ireland, but if the dramatic thriller "50 Dead Men Walking" was a color, it would be gray, not green.

That's the dominant hue - or non-hue, as it were - in the color palette of director Kari Skogland's gritty version of 1988 Belfast, Ireland. It also happens to be the dominant characteristic of the morals at work in her story, one of the more absorbing and riveting portraits of The Troubles since 1993's "In the Name of the Father."

Marked by fine performances from Ben Kingsley ("Elegy," "Transsiberian") and rising English star Jim Sturgess ("21," "Crossing Over"), it's a taut, fast-starting story, based loosely on real events, about a teenage Irish firebrand who was recruited by British intelligence to provide inside information on the Irish Republican Army.

That kid, Martin McGartland (Sturgess), would eventually agree to help, and he would save lives in the process. The 50 men in the title represent the approximate number of deaths that were averted by his cooperation with police -- before, that is, the IRA caught wind of his extra-curricular activities and decided to put a violent end to it.

Jim Sturgess, left, and Ben Kingsley in 'Fifty Dead Men Walking.'

FIFTY DEAD MEN WALKING3 stars, out of 4

Snapshot: A dramatic thriller about an Irish teenager recruited by British intelligence forces to spy on the Irish Republican Army in 1988.

What works: Jim Sturgess delivers an intense performance, in what ends up being a fast-paced and absorbing film.

What doesn't: His character's motivations are a touch unclear, which gets in the way of the story.

It's a frighteningly realistic -- and, at times, violently frank -- image of the war on terror that dominated headlines long before the U.S.-led one in Afghanistan and Iraq. Exactly who the terrorists were, however, depends on whom you ask.

British officials would say it was the Irish Republican Army, with their car bombs and stashes of guns that they used in their guerrilla effort to end a nearly 40-year occupation of Northern Ireland by British forces. The IRA and their sympathizers, however, would say that they're freedom fighters, and that the real terrorists, before a power-sharing deal was struck in 2007, were the Queen's occupying forces.

Like I said, shades of gray.

Given the sensitive, divisive nature of the politically charged subject matter, "50 Dead Men Walking" is one of those movies -- like "Che" earlier this year, and "W." last year -- that is bound to stir up controversy in certain circles, no matter how well-assembled. Even the real McGartland, whose book inspired the film -- and who, 20 years later, is still in hiding -- has voiced a certain amount of displeasure with Skogland's retelling. Of particular concern is what he sees as a sympathetic portrayal of the IRA.

Rather than focusing on the murky nature of it all, Skogland instead tells a fairly straightforward story of a man caught in the middle of it all and who is struggling to do the right thing.

It starts in 1988 Belfast, which, as Sturgess points out in a voiceover, was a time and place in which "jobs were controlled by the Protestants, which meant most of the young Catholic men were unemployed -- and angry about it."

Being one of those Catholics, and being a tough and loyal one at that, McGartland was an attractive recruit for the IRA. He also had a conscience, however, which was tested by the daily brutality he witnessed. That made him an equally attractive recruit for British intelligence.

As McGartland's handler in the British police, Kingsley is as reliable as ever. The real story here is Sturgess, who, with just a handful of films under his belt, continues to impress, delivering a convincing blend of charm and intensity as McGartland.

Still, his Marty is a hard lad to figure out in writer-director Skogland's version of the story, which is built upon a script that makes his motivations a touch cloudy, from a narrative standpoint.

He seems genuinely happy to be part of the IRA, a fatherless kid who forges a father-son bond with one of his superiors. At the same time, however, he seems just as happy to be helping the police, forging another paternal bond with his handler and exhibiting not a shred of guilt for betraying the cause and his brothers fighting it.

Is he a hero, or is he just wishy-washy? Skogland seems to believe that it's the former, but her script never convincingly dispenses with the possibility of the latter.

Despite that, and despite the fact that Skogland's solidly directed story doesn't shed a whole lot of fresh light on the conflict, it is still a compelling and remarkable edge-of-your-seat tale.

Where that is concerned, at least, there are no shades of gray involved.